In a conventional mobile communication system, in an uplink from a mobile station UE to a radio base station Node B, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel, in consideration of radio resources of the radio base station Node B, an interference volume in an uplink, transmission power of the mobile station UE, transmission processing performance of the mobile station UE, a transmission rate required for an upper application, and the like, and to notify the determined transmission rate of the dedicated channel by a message in a layer-3 (Radio Resource Control Layer) to both of the mobile station UE and the radio base station Node B.
Here, the radio network controller RNC is provided at an upper level of the radio base station Node B, and is an apparatus configured to control the radio base station Node B and the mobile station UE.
In general, data communications often cause burst traffic compared with voice communications or TV communications. Therefore, it is preferable that a transmission rate of a channel used for the data communications is changed fast.
However, as shown in FIG. 10, the radio network controller RNC integrally controls a plurality of radio base stations Node B in general. Therefore, in the conventional mobile communication system, there has been a problem that it is difficult to perform fast control for changing of the transmission rate of channel (for example, per approximately 1 through 100 ms), due to processing load, processing delay, or the like.
In addition, in the conventional mobile communication system, there has also been a problem that costs for implementing an apparatus and for operating a network are substantially increased even if the fast control for changing of the transmission rate of the channel can be performed.
Therefore, in the conventional mobile communication system, control for changing of the transmission rate of the channel is generally performed on the order from a few hundred ms to a few seconds.
Accordingly, in the conventional mobile communication system, when burst data transmission is performed as shown in FIG. 11(a), the data are transmitted by accepting low-speed, high-delay, and low-transmission efficiency as shown in FIG. 11(b), or, as shown in FIG. 11(c), by reserving radio resources for high-speed communications to accept that radio bandwidth resources in an unoccupied state and hardware resources in the radio base station Node B are wasted.
It should be noted that both of the above-described radio bandwidth resources and hardware resources are applied to the vertical radio resources in FIG. 11.
Therefore, the 3rd Generation Partnership Project (3GPP) and the 3rd Generation Partnership Project 2 (3GPP2), which are international standardization organizations of the third generation mobile communication system, have discussed a method for controlling radio resources at high speed in a layer-1 and a media access control (MAC) sub-layer (a layer-2) between the radio base station Node B and the mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter referred to as “Enhanced Uplink (EUL)”.
Radio resource control methods that have been discussed in the “Enhanced Uplink” can be broadly categorized into three as follows. The radio resource control methods will be briefly described below.
First, a radio resource control method that is referred to as “Time & Rate Control” has been discussed.
In such a radio resource control method, a radio base station Node B determines a mobile station UE which can transmit user data and a transmission rate of user data per a predetermined timing, so as to notify a mobile station ID as well as the information relating the transmission rate of user data (or a maximum allowable transmission rate of user data).
The mobile station UE designated by the radio base station Node B transmits user data at the designated timing and the transmission rate (or within a range of the maximum allowable transmission rate).
Second, a radio resource control method that is referred to as “Rate Control per UE” has been discussed.
In such a radio resource control method, if user data to be transmitted to the radio base station Node B exists, each mobile station UE can transmit the user data. However, regarding the maximum allowable transmission rate of the user data, the transmission rate determined by the radio base station Node B and notified to each mobile station UE for each transmission frame or each of a plurality of transmission frames, is used.
Here, when the maximum allowable transmission rate is notified, the radio base station Node B notifies the maximum allowable transmission rate itself at the timing, or a relative value thereof (for example, an “Up command”, a “Down command”, and a “Hold command”).
Third, a radio resource control method that is referred to as “Rate Control per Cell” has been discussed.
In such a radio resource control method, a radio base station Node B notifies a transmission rate of user data, which is common among mobile stations UE in communication, or information required to calculate the transmission rate, so that each mobile station UE determines a transmission rate of user data based on the received information.
Ideally, the “Time & Rate Control”, and the “Rate Control per UE” can be the best control methods for improving radio capacity in an uplink. However, a transmission rate of user data has to be granted after data volume stored in buffers of the mobile station UE, transmission power in the mobile station UE, or the like are grasped. Therefore, there has been a problem that control load is increased by the radio base station Node B.
In addition, in these radio resource control methods, there has been a problem that overhead becomes larger by exchanges of control signals.
On the other hand, in the “Rate Control per Cell”, there is an advantage in that control load by the radio base station Node B is small since the radio base station Node B notifies information which is common in cells, and each mobile station UE autonomously seeks the transmission rate of user data based on the received information.
However, the radio base station Node B has to be configured in such a manner that the user data in the uplink from any mobile station UE can be received. Therefore, there has been a problem that an apparatus size of radio base station Node B becomes large to effectively utilize the radio capacity of the uplink.
Accordingly, there has been proposed, for example, a scheme (Autonomous ramping method) that the mobile station UE increases the transmission rate of user data from a pre-notified initial transmission rate in accordance with predetermined rules so that excessive allocation of radio capacity by the radio base station Node B can be prevented, thereby preventing increase of the apparatus size of radio base station Node B, as described in Non-patent Document 1.
In such a scheme, a radio base station Node B determines a maximum allowable transmission rate (or a parameter relating to the maximum allowable transmission rate, the same shall apply hereinafter) based on hardware resources or radio bandwidth resources (for example, an interference volume in an uplink) in each cell, so as to control the transmission rate of user data in communicating mobile stations UE. Detailed descriptions of a control scheme based on hardware resources and a control scheme based on an interference volume in an uplink will be given below.
In the control scheme based on the hardware resources, a radio base station Node B is configured to notify a maximum allowable transmission rate to a mobile station UE connected to a cell under the control thereof.
The radio base station Node B lowers the maximum allowable transmission rate so as to avoid shortage of the hardware resources when the transmission rate of user data in the mobile station UE connected to the cell under the control thereof is increased and the hardware resources are insufficient.
On the other hand, the radio base station Node B again increases the maximum allowable transmission rate when the space of the hardware resources becomes larger, such as when the user data transmission in the mobile station UE connected to the cell under the control thereof has been completed, or the like.
In addition, in the control scheme based on the interference volume in the uplink, a radio base station Node B is configured to notify a maximum allowable transmission rate to a mobile station UE connected to a cell under the control thereof.
When the transmission rate of user data in the mobile station UE connected to the cell under the control of a radio base station Node B increases and a measured interference volume (for example, a measured noise rise) in the uplink exceeds an allowable value (for example, a maximum allowable noise rise), the radio base station Node B lowers the maximum allowable transmission rate so that the interference volume in the uplink can be within a range of the allowable value (see, FIG. 12).
On the other hand, when the interference volume (for example, the noise rise) in the uplink is within a range of the allowable value (for example, the maximum allowable noise rise) thereby having a space, such as when the user data transmission in the mobile station UE connected to the cell under the control of the radio base station Node B has been completed, or the like, the radio base station Node B again increases the maximum allowable transmission rate (see, FIG. 12).
Further, a transmission power control in a mobile communication system using “EUL” will be described with reference to FIG. 13.
A transmitter 101 of the mobile station UE is configured to periodically transmit a Dedicated Physical Control Channel (DPCCH), to which a layer-1 control information such as a pilot signal, a TPC command or the like are mapped.
In addition, the transmitter 101 of the mobile station UE is configured to transmit a Dedicated Physical Data Channel (DPDCH) or an Enhanced Dedicated Physical Data Channel (E-DPDCH), to which the uplink user data or the control information in more than layer 2 are mapped, in accordance with presence or absence of uplink user data to be transmitted, or presence or absence of a transmission opportunity allocation.
An SIR calculating section 202 of the radio base station Node B calculates a reception signal to interference power ratio (a reception SIR) of the control signal received through the DPCH, and compares a set target SIR with the reception SIR.
When the reception SIR is larger than the target SIR, a transmitter 203 of the radio base station Node B transmits a “Down” command to the mobile station UE. When the reception SIR is smaller than the target SIR, the transmitter 203 of the radio base station Node B transmits an “Up” command to the mobile station UE.
A series of operation described above is referred to as an “inner loop transmission power control”.
On the other hand, an input section 301 of the radio network controller RNC is configured to measure a reception quality of the E-DPDCH (or the DPDCH).
Then, a controller 302 of the radio network controller RNC is configured to set a target SIR of the radio base station Node B based on the measurement result, and to determine a transmission wave amplitude ratio between the E-DPDCH transmitted from the mobile station UE and the DPCCH (the above transmission amplitude ratio is hereinafter referred to as “gain factor”), so as to notify the determined gain factor to the mobile station UE.
A series of operation described above is referred to as “outer loop transmission power control”.
In the conventional mobile communication system using “EUL”, “outer loop transmission power control” can be adapted to various fluctuations in radio environment, such as when the mobile station UE shifts to soft handover status, when the transmission rate of the mobile station UE has changed, when the radio waves are interrupted by such as buildings, or the like.
However, if user data to be transmitted through the E-DPDCH does not exist, only “inner loop transmission power control” is performed without “outer loop transmission power control”. In such a case, the gain factor or the target SIR cannot be set appropriately in accordance with the propagation environment changing, thereby it is not possible to transmit uplink user data with an appropriate transmission power when the transmission is restarted. This causes a problem of deterioration in the radio quality.    (Non-patent Document 1) 3GPP TSG-RAN R2-042010